Field of the Invention
The present invention relates to an oil-based inkjet ink set and a method for producing a printed item.
Description of the Related Art
The inkjet recording method is a method in which an inkjet ink of high fluidity is jetted from fine nozzles in the form of liquid droplets, thus recording an image on a recording medium positioned facing the nozzles, and because this method enables high-speed printing to be conducted with minimal noise, it has rapidly become widespread in recent years. Examples of known types of inks that can be used in this type of inkjet recording method include aqueous inks which contain water as the main solvent, ultraviolet-curable inks (UV inks) which contain a large amount of a polymerizable monomer as the main component, hot melt inks (solid inks) which contain a large amount of a wax as the main component, and so-called non-aqueous inks which contain a non-aqueous solvent as the main solvent. Non-aqueous inks can be classified into solvent-based inks in which the main solvent is a volatile organic solvent, and oil-based inks in which the main solvent is an organic solvent having either low volatility or no volatility. Solvent-based inks mainly dry on the recording medium as a result of evaporation of the organic solvent, whereas oil-based inks mainly dry as a result of penetration into the recording medium.
With an oil-based ink, when a paper is used as the recording medium, because the effect on the bonds between the pulp fibers that constitute the structural component of the paper is small, the printed paper is unlikely to suffer from curling or cockling, and because penetration of the ink into the paper is rapid, the apparent drying properties are excellent. Moreover, oil-based inks also offer the advantages that because the solvent is difficult to volatilize, nozzle blockages are unlikely to occur, and the frequency of head cleaning can be reduced, making the inks applicable to high-speed printing.
On the other hand, with oil-based inks, because the coloring material in the ink penetrates into the paper, achieving a high print density is difficult, and because the ink typically does not contain a component for fixing the coloring material, if any of the coloring material remains on the surface of the recording medium, it tends to be prone to detachment or transfer.
Further, if printing is performed over a long period using an oil-based inkjet ink in an inkjet printer, then metal salts and the like included in the ink raw materials may sometimes be deposited as solids in the vicinity of the nozzles of the inkjet head, hindering normal discharge and causing image faults. In response to these types of problems, a method in which the amounts of specific metals in the ink are limited to amounts no greater than specified numerical values, and a method for producing an ink in which, without removing the problematic metal compounds, a specific pigment dispersant and/or organic solvent and a fixing resin are dispersed in an organic solvent containing a compound having a specific structure have been proposed (JP 2010-270220 A and JP 2011-089043 A).